• 한국기계가공학회지
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• 제19권5호
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• pp.27-37
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• 2020

Structural optimization problems with discrete design variables require more function calculations (or finite element analyses) than those in the continuous design space. In this study, a method to find an optimal solution in the discrete design of the truss structure is presented, reducing the number of function calculations. Because a continuous optimal solution is the Karush-Kuhn-Tucker point that satisfies the optimality condition, it is assumed that the discrete optimal solution is around the continuous optimum. Then, response values such as weight, displacement, and stress are predicted using approximate models-referred to as hybrid metamodels-within specified design ranges. The discrete design method using the hybrid metamodels is used as a post-process of the continuous optimization process. Standard truss design problems of 10-bar, 25-bar, 15-bar, and 52-bar are solved to show the usefulness of this method. The results are compared with those of existing methods.

• 한국미생물생명공학회:학술대회논문집
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• 한국미생물생명공학회 2005년도 2005 Annual Meeting & International Symposium
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• pp.233-244
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• 2005

Guanosine fermentation process can be well predicted and analyzed by the proposed state equations describing the dynamic change of a bioreactor. Pyruvate and alanine were found to be characteristically accumulated along with the decline of the guanosine formation rate during the mid-late phase of the process. The enzymological study of the main pathways in glucose catabolism and the quantitative stoichiometric calculation of metabolic flux distribution revealed that it was entirely attributed to the shift of metabolic flux from hexose monophosphate (HMP) pathway to glycolysis pathway. The process optimization by focusing on the restore of the shift of metabolic flux was conducted and the overcoming the decrease of oxygen uptake rate (OUR) was taken as the relevant factor of the trans-scale operation. As a result, the production of guanosinewas increased from 17 g/L to over 34 g/I.

• International Journal of Korean Welding Society
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• 제3권2호
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• pp.15-23
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• 2003

A genetic algorithm was applied to an arc welding process to determine near optimal settings of welding process parameters which produce good weld quality. This method searches for optimal settings of welding parameters through systematic experiments without a model between input and output variables. It has an advantage of being able to find optimal conditions with a fewer number of experiments than conventional full factorial design. A genetic algorithm was applied to optimization of weld bead geometry. In the optimization problem, the input variables were wire feed rate, welding voltage, and welding speed, root opening and the output variables were bead height, bead width, penetration and back bead width. The number of level for each input variable is 8, 16, 8 and 3, respectively. Therefore, according to the conventional full factorial design, in order to find the optimal welding conditions, 3,072 experiments must be performed. The genetic algorithm, however, found the near optimal welding conditions from less than 48 experiments.

• Journal of Welding and Joining
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• 제18권5호
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• pp.63-69
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• 2000

A genetic algorithm was applied to an arc welding process to determine near optimal settings of welding process parameters which produce good weld quality. This method searches for optimal settings of welding parameters through systematic experiments without a model between input and output variables. It has an advantage of being able to find optimal conditions with a fewer number of experiments than conventional full factorial design. A genetic algorithm was applied to optimization of weld bead geometry. In the optimization problem, the input variables was wire feed rate, welding voltage, and welding speed and the output variables were bead height, bead width, and penetration. The number of level for each input variable is 16, 16, and 8, respectively. Therefore, according to the conventional full factorial design, in order to find the optimal welding conditions, 2048 experiments must be performed. The genetic algorithm, however, found the near optimal welding conditions from less than 40 experiments.

• International Journal of Korean Welding Society
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• 제1권1호
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• pp.44-50
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• 2001

A genetic algorithm was applied to the arc welding process as to determine the near-optimal settings of welding process parameters that produce the good weld quality. This method searches for optimal settings of welding parameters through the systematic experiments without the need for a model between the input and output variables. It has an advantage of being capable to find the optimal conditions with a fewer number of experiments rather than conventional full factorial designs. A genetic algorithm was applied to the optimization of the weld bead geometry. In the optimization problem, the input variables were wire feed rate, welding voltage, and welding speed. The output variables were the bead height bead width, and penetration. The number of levels for each input variable is 16, 16, and 8, respectively. Therefore, according to the conventional full factorial design, in order to find the optimal welding conditions,2048 experiments must be performed. The genetic algorithm, however, found the near optimal welding conditions in less than 40 experiments.

• 대한기계학회논문집A
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• 제29권2호
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• pp.333-340
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• 2005

Feedrate is one of the factors that have the significant effects on the productivity, qualify and tool life in the cutting mechanism as well as cutting velocity, depth of cut and width of cut. In this study, in order to realize the high-efficient machining, a new feedrate optimization method is proposed based on the concept that the optimum feedrate can be derived from the allowable cutting power since the cutting power can be predicted from the cutting parameters as feedrate, depth of cut, width of cut, chip thickness, engagement angle, rake angle, specific cutting force and so on. Tool paths are extracted from the original NC program via the reverse post-processing process and converted into the infinitesimal tool paths via the interpolation process. And the novel NC program is reconstructed by optimizing the feedrate of infinitesimal tool paths. Especially, the fast feedrate optimization is realized by using the Boolean operation based on the Goldfeather CSG rendering algorithm, and the simulation results reveal the availability of the proposed optimization method dramatically reducing the cutting time and/or the optimization time. As a result, the proposed optimization method will go far toward improving the productivity and qualify.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 추계학술대회논문집
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• pp.248-251
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• 2006

This paper provides the basic theory and numerical results of shell design optimization considering the appearance of close natural frequencies in optimization process. In this study the fundamental natural frequency to be maximized is considered as the objective function and the initial volume of structures is used as the constraint function. In addition, the constraints related to natural frequency is also adopted to avoid the natural frequency closeness phenomenon during the optimization iteration. The Coon's patch is used to represent the shape and thickness distribution of shells. A degenerated shell finite element is adopted to calculate the fundamental natural frequency of the shells. The SQP available in the optimizer DoT is used to search optimum solution. From numerical results, the introduction of the frequency constraint into shell design optimization can deeply affect on the final optimum shape of shells although it is likely to be used to avoid the frequency closeness phenomenon.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.1234-1239
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• 2003

In the product design process computer-aided engineering and optimization tools are widely utilized in order to reduce the total development time and cost. Since several simulation tools are involved in the process, information losses, omissions, or errors are common and the importance of seamless information exchange among the tools has been increased. In this study ISO STEP standards are adopted to represent the neutral format for CAE/CAO information exchange. The schema of AP209 is used to define the information of finite element analysis and the new schema is proposed to describe the information of structural optimization based on the STEP methodology. The schema is implemented by EXPRESS, information modeling language, and ST-Developer is employed to generate C++ classes and STEP Rose Library by using the schema denoted. To substantiate the proposed approach, the information access interfaces of the finite element modeling software (FEMAP), structural optimization software (GENESIS) and in-house topology optimization program are developed. Examples of the size optimization of a three-bar truss and topology optimization of a MBB beam are shown to validate the information exchange of finite element analysis and structural optimization using STEP standards.

• 한국해양공학회지
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• 제34권4호
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• pp.272-276
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• 2020

This paper presents an optimization process for a catamaran hull form. The entire optimization process was managed using the CAD-CFD integration platform CAESES. The resistance of the demi-hull was simulated in calm water using the CFD solver STAR-CCM+, and an inviscid fluid model was used to reduce the computing time. The Free-Form Deformation (FFD) method was used to make local changes in the bulbous bow. For the optimization of the bulbous bow, the Non-dominated Sorting Genetic Algorithm (NSGA)-II was applied, and the optimization variables were the length, breadth, and angle between the bulbous bow and the base line. The Lackenby method was used for global variation of the bow of the hull. Nine hull forms were generated by moving the center of buoyancy while keeping the displacement constant. The optimum bow part was selected by comparing the resistance of the forms. After obtaining the optimum demi-hull, the distance between two demi-hulls was optimized. The results show that the proposed optimization sequence can be used to reduce the resistance of a catamaran in calm water.

• 한국전산구조공학회논문집
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• 제16권1호
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• pp.59-68
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• 2003

본 연구를 통하여 다하중 경우를 가지는 평면구조물의 위상을 도출하기 위한 최적화 프로그램을 개발하였다. 계산시간을 줄이고 실용적인 위상최적화를 수행하기 위하여 사절점 저차 유한요소를 이용하였다. 저차 유한요소를 사용하여 도출되는 위상에 나타나는 체크무늬현상을 제거하기 위해 여과절차를 도입하였다. 위상최적화를 수행하기 위하여 가등질화된 물질로 구조재를 표현하였고 물질을 재분배하기 위하여 최적정기준을 바탕으로 유도한 크기조절 알고리듬을 도입하였다. 개발된 프로그램을 이용하여 단하중 경우와 다하중 경우에 대한 평면 구조물의 위상을 도출하고 이를 비교분석하였다. 본 연구를 통하여 구조물의 실제적인 위상을 도출하기 위해서는 다하중 경우가 반드시 고려되어야 하는 것으로 나타났다.